1. Field of the Invention
This invention relates to magnetic transducers for use in sensing speed or position.
2. Prior Art
Various crankshaft position sensors are known for engine speed measurement and control of ignition timing in an internal combustion engine. Typically, the sensor provides an output signal based on movement of a crankshaft pulse ring. For example, the crankshaft sensor can include a permanent magnet and a wound wire coil mounted adjacent the crankshaft pulse ring to sense changing magnetic flux. When the crankshaft rotates, individual pulse ring lobes from the crankshaft pulse ring approach, align with and then pass the crankshaft sensor. As the metal lobes pass through the sensor's magnetic field, the field distortion which occurs causes the turns of the wire coil to be cut by magnetic flux, or the coil to be threaded by the magnetic flux, so as to generate a voltage output signal of crankshaft position which can be used by an engine control computer. Sensor voltage increases, then sharply decreases and returns to base level, each time a lobe crosses the sensor's magnetic field. The computer interprets the pulses of voltage inputs as crankshaft position for spark timing. It can also decode engine speed information for spark advance calculation.
To provide a sensor output of adequate magnitude, many coil turns are required. Producing such a wound wire coil with associated electrical terminations is relatively expensive and time consuming. It would be desirable to reduce cost and to produce a sensor using high volume batch processing fabrication techniques.
U.S. Pat. No. 3,549,825 issued to Trimble teaches a magnetic transducer for use in magnetic recording and reproduction. The coil structure disclosed in this patent is a relatively complicated structure requiring about sixty-one distinct processing steps. Several are critical steps which could result in overetching or overabrading. A sputter deposited coil is fabricated in the general shape of a spiral with at least a portion of the coil being sandwiched between the pole ends of two magnetic circuit plates. The goals of this design are high resolution and high switch rate capability so that the transducer is able to orient or sense magnetic domains on a recording disc or tape surface rotating at high speed. In an automotive application to sense crankshaft position, much higher signal levels would be required from the transducer element, in a much more harsh operating environment. The positioning of the sensor adjacent the crankshaft cannot be as close as the positioning of a recording head to the recording disc or tape surface. As a result, the magnetic field intensity and extension into the gap between the sensor and the crankshaft must both be much greater for the automotive application than for the recorder read-write head. The magnetic field generated by powering up the tiny coil would be inadequate for the automotive application and the sensor must provide a strong magnetic field with a permanent magnet.
U.S. Pat. No. 4,166,977 issued to Glauert et al teaches a rotary speed and angular position determination system used for the crankshaft of an internal combustion engine. This patent generally teaches the sensing element as being one of a number of alternatives including coils, Hall generators, field responsive diodes, field responsive chips or the like. It does not teach a planar coil sensor structure or method of making such a structure. It would be desirable to have a low cost, batch produced magnetic transducer suitable for automotive lobe, gear tooth, or gap sensing applications.